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</pre><pre class="rust ">
<span class="comment">// string_collection.rs</span>
<span class="comment">// </span>
<span class="comment">// This file is part of the Eclipse Paho MQTT Rust Client library.</span>
<span class="comment">//</span>
<span class="comment">// A string_collection is a helper to bridge between a collection of </span>
<span class="comment">// strings in Rust to an array of NUL terminated char string pointers that</span>
<span class="comment">// the C library expects.</span>
<span class="comment">//</span>
<span class="comment">// It is useful when a C API takes a `const char *arg[]` parameter.</span>
<span class="comment">//</span>

<span class="comment">/*******************************************************************************
 * Copyright (c) 2017 Frank Pagliughi &lt;fpagliughi@mindspring.com&gt;
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Eclipse Distribution License v1.0 which accompany this distribution.
 *
 * The Eclipse Public License is available at
 *    http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 *   http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *    Frank Pagliughi - initial implementation and documentation
 *******************************************************************************/</span>

<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ffi</span>::{<span class="ident">CString</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">os</span>::<span class="ident">raw</span>::{<span class="ident">c_char</span>};

<span class="doccomment">/// A collection of C-compatible (NUL-terminated) strings that is useful with</span>
<span class="doccomment">/// C API&#39;s that require an array of strings, normally specified as:</span>
<span class="doccomment">/// `const char* arr[]` or  `const char** arr`</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">StringCollection</span>
{
	<span class="doccomment">/// The owned NUL-terminated strings</span>
	<span class="ident">coll</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">CString</span><span class="op">&gt;</span>,
	<span class="doccomment">/// A vector cache of pointers into `coll`</span>
	<span class="doccomment">/// This must be updated any time `coll` is modified.</span>
	<span class="ident">c_coll</span>: <span class="ident">Vec</span><span class="op">&lt;</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">c_char</span><span class="op">&gt;</span>,
}

<span class="kw">impl</span> <span class="ident">StringCollection</span>
{
	<span class="doccomment">/// Creates a StringCollection from a vector of strings.</span>
	<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">coll</span>: <span class="kw-2">&amp;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">StringCollection</span> {
		<span class="kw">let</span> <span class="ident">sc</span> <span class="op">=</span> <span class="ident">StringCollection</span> {
			<span class="ident">coll</span>: <span class="ident">StringCollection</span>::<span class="ident">to_cstring</span>(<span class="ident">coll</span>),
			<span class="ident">c_coll</span>: <span class="ident">Vec</span>::<span class="ident">new</span>(),
		};
		<span class="ident">StringCollection</span>::<span class="ident">fixup</span>(<span class="ident">sc</span>)
	}

	<span class="comment">// Convert a vector of strings to a vector of CStrings.</span>
	<span class="kw">fn</span> <span class="ident">to_cstring</span>(<span class="ident">coll</span>: <span class="kw-2">&amp;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">String</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">CString</span><span class="op">&gt;</span> {
 		<span class="ident">coll</span>.<span class="ident">iter</span>()
			.<span class="ident">map</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="ident">CString</span>::<span class="ident">new</span>(<span class="ident">s</span>.<span class="ident">as_str</span>()).<span class="ident">unwrap</span>())
			.<span class="ident">collect</span>()
	}

	<span class="comment">// Convert a vector of CString&#39;s to a vector of C char pointers.</span>
	<span class="comment">// Note that the pointers are invalidated if the original vector or</span>
	<span class="comment">// any of the strings in it change.</span>
	<span class="kw">fn</span> <span class="ident">to_c_vec</span>(<span class="ident">sv</span>: <span class="kw-2">&amp;</span><span class="ident">Vec</span><span class="op">&lt;</span><span class="ident">CString</span><span class="op">&gt;</span>) <span class="op">-&gt;</span> <span class="ident">Vec</span><span class="op">&lt;</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">c_char</span><span class="op">&gt;</span> {
		<span class="ident">sv</span>.<span class="ident">iter</span>()
			.<span class="ident">map</span>(<span class="op">|</span><span class="ident">cs</span><span class="op">|</span> <span class="ident">cs</span>.<span class="ident">as_ptr</span>())
			.<span class="ident">collect</span>()
	}

	<span class="comment">// Updates the cached vector to correspond to the string.</span>
	<span class="kw">fn</span> <span class="ident">fixup</span>(<span class="kw-2">mut</span> <span class="ident">coll</span>: <span class="ident">StringCollection</span>) <span class="op">-&gt;</span> <span class="ident">StringCollection</span> {
		<span class="ident">coll</span>.<span class="ident">c_coll</span> <span class="op">=</span> <span class="ident">StringCollection</span>::<span class="ident">to_c_vec</span>(<span class="kw-2">&amp;</span><span class="ident">coll</span>.<span class="ident">coll</span>);
		<span class="ident">coll</span>
	}

	<span class="doccomment">/// Gets the number of strings in the collection.</span>
	<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">usize</span> {
		<span class="self">self</span>.<span class="ident">coll</span>.<span class="ident">len</span>()
	}

	<span class="doccomment">/// Gets the collection as a pointer to C string pointers.</span>
	<span class="doccomment">/// This returns a pointer that can be sent to a C API that takes a </span>
	<span class="doccomment">/// pointer to an array of char pointers, like `const char* arr[]`</span>
	<span class="doccomment">/// This function is inherently unsafe. The pointer it returns is only</span>
	<span class="doccomment">/// valid while the collection remains unmodified. In general, it</span>
	<span class="doccomment">/// should be requested when needed and not stored for future use.</span>
	<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">as_c_arr_ptr</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">c_char</span> {
		<span class="self">self</span>.<span class="ident">c_coll</span>.<span class="ident">as_ptr</span>()
	}
}

<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">StringCollection</span>
{
	<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-&gt;</span> <span class="ident">StringCollection</span> {
		<span class="kw">let</span> <span class="ident">sc</span> <span class="op">=</span> <span class="ident">StringCollection</span> {
			<span class="ident">coll</span>: <span class="ident">Vec</span>::<span class="ident">new</span>(),
			<span class="ident">c_coll</span>: <span class="ident">Vec</span>::<span class="ident">new</span>(),
		};
		<span class="ident">StringCollection</span>::<span class="ident">fixup</span>(<span class="ident">sc</span>)
	}
}

<span class="kw">impl</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">StringCollection</span>
{
	<span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">StringCollection</span> {
		<span class="kw">let</span> <span class="ident">sc</span> <span class="op">=</span> <span class="ident">StringCollection</span> {
			<span class="ident">coll</span>: <span class="self">self</span>.<span class="ident">coll</span>.<span class="ident">clone</span>(),
			<span class="ident">c_coll</span>: <span class="ident">Vec</span>::<span class="ident">new</span>(),
		};
		<span class="ident">StringCollection</span>::<span class="ident">fixup</span>(<span class="ident">sc</span>)
	}
}


</pre>
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